Scheme plays a role in success, obviously. Just look at Belichick.
However, it comes down to players. In 2010, when Capers perhaps the best secondary the Packers have ever had (a HOFer in Woodson, two other Pro Bowl-level players (Collins and Tramon) and probably the best 3rd CB in the league (Shields), the defense was great. Not to mention Pickett, a peak level Raji, and C. Jenkins on the line and CM3 coming into his prime. Dom's schemes drive us nuts, but it really comes down to the fact that the ILBs and Randall/Rollins/Gunther haven't been good enough. Maybe that's talent, maybe it's coaching, but there is a lot of evidence they aren't good enough to beat good teams with. If you replace the 2016 team with the same level of talent as the 2010 team, they'll probably look great again.
Many of us have deified Fritz Shurmur for when he was the DC during the mid-1990s. From 1990 to 1993, Shurmur coordinated some of the worst ranked defenses in the league for the Cards and Rams. He comes to Green Bay, gets to work with one of the best defensive lines in history (Reggie, Sean Jones, S. Dotson, and Gilbert Brown) and an outstanding secondary and he runs a dominant defense. It's usually about the players.
A bad defensive coordinator takes good talent and schemes them to be lesser than the sum of their parts. We've seen many of these.
A good defensive coordinator takes good talent and doesn't screw it up.
A HOF-level DC takes good to great talent and makes it elite.
I'd say Dom is in category 2.